IRQ
Short for Interrupt ReQuest and pronounced as I-R-Q, IRQ is a signal that has a direct line to the computer processor allowing it to stop the processor momentarily and decide what to do next. IBM compatible computers go up to IRQ 15, and are prioritized in the computer according to the importance of the device. Today, most users will never need to worry about IRQ settings because all devices are now PnP and configured automatically. Below is an overview of the traditional IBM IRQ's, I/O ports, and their related devices.
| IRQ | DEVICE | I/O PORT | BUS SLOT | CARD Type |
|---|---|---|---|---|
| 00 | System Timer | None | NO | NONE |
| 01 | Keyboard | None | NO | NONE |
| 02 | Cascade Controller 2nd PIC |
None | NO | NONE |
| 03 | COM 2 and 4 | COM 2: 02F8h (02F8 or 2F8) COM 4: 02E8h (02E8 or 2E8) |
YES | 8 or 16-BIT |
| 04 | COM 1 and 3 | COM 1: 03F8h (03F8 or 3F8) COM 3: 03E8h (03E8 or 3E8) |
YES | 8 or 16-BIT |
| 05 | Sound Parallel Port 2 |
PARALLEL PORT 2: 0278h - 0378h |
YES | 8 or 16-BIT |
| 06 | Floppy | 03F0 - 03F5 | YES | 8 or 16-BIT |
| 07 | Parallel Port 1 | 0278h - 0378h | YES | 8 or 16-BIT |
| 08 | Real-time Clock | None | NO | NONE |
| 09 | Redirected IRQ 2 Open Network Available |
None | YES | 8 or 16-BIT |
| 10 | Open | None | YES | 8 or 16-BIT |
| 11 | Open SCSI Video |
VIDEO: 3B0-3DF |
YES | 8 or 16-BIT |
| 12 | Open PS2 |
None | YES | 8 or 16-BIT |
| 13 | Coprocessor | None | NO | NONE |
| 14 | Open Primary hard drive (master) Hard Drive Controller |
1ST IDE: 1F0 | YES | 8 or 16-BIT |
| 15 | Open 2nd hard drive (slave) |
2ND IDE: 170 | YES | 8 or 16-BIT |
Tip: Technically there are 16 IRQs if you count IRQ 0, the system timer and all IRQs above 15 are known as virtual IRQs and are assigned and handled by the operating system and APIC.
Also see: DMA, Hardware conflict, I/O port, Interrupts, IRQL